1. Field of the Invention
The present invention relates to an ink reservoir which stores an ink supplied to a recording head employed in an ink jet recording field, an ink jet head structure including the ink reservoir, and an ink jet recording apparatus including the ink reservoir. More specifically, the present invention relates to an ink jet head structure including an ink reservoir which structure adopts an intermittent ink supply system mounted on a carriage of the ink jet recording apparatus with an ink jet recording head, connected to a main ink tank at need and intermittently supplied with an ink and to an ink jet recording apparatus including the ink reservoir.
2. Related Background Art
As an ink jet recording apparatus that records data while scanning an ink jet recording head, there is known a so-called on-carriage type ink jet recording apparatus where an ink jet recording head 201 having a nozzle which discharges an ink is connected to an ink tank which stores and holds the ink supplied to the head 201 and which has an air communication section having an interior opened to the air, the resultant connected head and tank are mounted on a carriage 201a in a cartridge state in which a head cartridge 201b is detachably attachable to the carriage (in which state the recording head and the ink tank can be provided either integrally or separably), and the carriage 201a allows the head cartridge 201b to perform scanning and recording along a guide shaft 208 as shown in FIG. 11.
As shown in FIG. 12, there is also known a so-called tube supply type ink jet recording apparatus where only an ink jet recording head 301 is provided on a carriage 301a, a tank cartridge 301c which stores an ink is provided on a main body side, and the ink is supplied to the ink jet recording head 301 by connecting the head 301 to the tank cartridge 301c by a flexible ink supply tube 301d. 
However, the on-carriage type apparatus as shown in FIG. 11 has the following disadvantages. Since the head cartridge 201b which holds the ink therein is provided on the carriage 201a, the weight of the apparatus is disadvantageously heavy and the heavy weight hampers high rate scanning of the cartridge 201a. In addition, if the head cartridge. 201b is made small in size so as to reduce the weight of the apparatus, the number of sheets on which data can be recorded disadvantageously decreases.
The tube supply type apparatus as shown in FIG. 12 has the following disadvantages. A mechanism of the apparatus is disadvantageously complicated since the ink cartridge 301c provided on the main body side is connected to the ink jet recording head 301 by the ink supply tube 301d, with the result that it is disadvantageously difficult to make the apparatus small in size.
To overcome these disadvantages, there is proposed an intermittent ink supply type (which will be often referred to as “pit-in type” for the sake of convenience) apparatus where a recording head having a sub-tank is provided on a carriage, the recording head is connected to a main tank provided on an apparatus main body at need when the carriage is at a home position or a predetermined position to thereby supply a predetermined amount of ink to the sub-tank on the carriage.
FIG. 13 is a schematic diagram which illustrates one example of the pit-in type ink jet recording apparatus (see Japanese Patent Application Laid-Open No. H8-112913).
As shown in FIG. 13, a recording head 401 that records data on a recording sheet 420 carried by a paper feed roller 421 is mounted on a carriage 401a. This carriage 401a is constituted to be guided by a guide shaft 408. A main tank 404 which replenishes a sub-tank 403 of the recording head 401 with an ink is arranged at a home position 423. This main tank 404 is provided with a supply tube 410 connected with an ink supply port 411 of the sub-tank 403. A dummy cap 406 which seals and protects an ink jet recording element, an absorbing cap 405 which absorbs the ink from a nozzle of the ink jet recording element, and an air intake cap 422 which absorbs air from an air hole 415 of the sub-tank 403 are provided to communicate with a negative pressure generator 407.
A pit-in operation of the pit-in type ink jet recording apparatus shown in FIG. 13 will next be described.
When the apparatus records no data, the ink jet recording head 401 waits at the home position 423 at which the head 401 is connectable to the absorbing cap 405, the air intake cap 422, the dummy cap 406, and the main tank 404. If a recording signal is transmitted to a recording apparatus main body, the dummy cap 406 seals a discharge port, not shown, of the ink jet recording element, and the supply tube 410 of the main tank 404 is connected to an ink supply port 411 of the sub-tank 403. The air intake cap 422 is then connected to the air hole 415 of the sub-tank 403 and the negative pressure generator 407 is actuated. The negative pressure generator 407 reduces an internal pressure of the sub-tank 403, whereby the ink is supplied from the main tank 404 to the sub-tank 403.
Next, a recovery operation is performed so as to prevent a backward flow of the ink in the nozzle toward the sub-tank 403 which flow occurs when the internal pressure of the sub-tank 403 is reduced or prevent poor discharge caused by clogging of the ink which viscosity is improved after the ink is left as it is for a long time. In this recovery operation, the air hole 415 and the ink supply port 411 of the sub-tank 403 are let open, the absorbing cap 405 is connected to the ink jet recording element, and the ink in the nozzle is absorbed by the negative pressure generator 407. After absorbing the ink, the ink adhering to a discharge port surface of the ink jet recording head 401 is wiped away (subjected to wiping), a pre-discharge for removing a mixed color ink forced into the nozzle by the wiping is performed, and then recording is started.
As can be seen, according to the pit-in type ink jet recording apparatus, since only the ink jet recording element and the sub-tank 403 are arranged on the carriage 401, the weight of the carriage 401 can be reduced. Therefore, the ink jet recording head 401 can be scanned at high rate. In addition, since the sub-tank 403 is replenished with the ink by the main tank 404 at the home position 423, the number of recording sheets can be increased. Further, since there is no need to connect carriage to the tank by the ink supply tube as required in the tube-supply type apparatus that employs the tank cartridge, the configuration of the apparatus can be advantageously made quite simple.
As an ink replenishment mechanism for replenishing the ink from the main tank to the sub-tank in this pit-in type ink jet recording apparatus, there is known a mechanism in which a sensor detects an ink amount by which the ink can be supplied to the sub-tan during the pit-in operation to thereby supply the ink to the sub-tank (see, for example, Japanese Patent Application Laid-Open No. H8-112913).
However, this mechanism is often quite complicated, delicate and expensive.
To solve these disadvantages, there is proposed a pit-in type ink jet recording apparatus having a gas-liquid separation member is arranged in the sub-tank. FIG. 14 is a schematic cross-sectional view illustrating one example of an ink jet recording head employed in the pit-in type ink jet recording apparatus that employs the gas-liquid separation member.
This ink jet recording head shown therein is mounted on the ink jet recording apparatus as shown in FIG. 13. An ink absorbing member 437 is arranged in an ink reservoir 436 which stores an ink. The gas-liquid separation member 433 is arranged halfway along a cap member 435 communicating with the air port 415. The gas-liquid separation member 433 is a porous member made of PTFE (polytetrafluoroethylene) or the like that transmits a gas but shuts off a liquid such as an ink.
An ink replenishment operation for replenishing the pit-in type ink jet recording head shown in FIG. 14 with the ink will next be described.
If a recording signal is transmitted to the recording apparatus main body, the dummy cap 406 seals the discharge port of the ink jet recording element 438 and the supply tube 410 of the main tank 404 is connected to the ink supply port 411 of the sub-tank 403. The absorbing cap 405 is connected to the air hole 415 of the sub-tank 403, and the negative pressure generator 407 is actuated to discharge the air in the ink reservoir 436 from the air hole 415 via the gas-liquid separation member 433. Accordingly, the internal pressure of the sub-tank 403 is reduced and the ink is continuously supplied to the sub-tank 403 from the main tank 404 through the supply tube 410 and the ink supply port 411 until the ink reservoir is filled with the ink. Right after the supply of the ink, the recovery operation, the wiping operation, and the initial pre-discharge operation are carried out as described with reference to FIG. 13, thereby turning a recording material into a state in which recording signals can be recorded on the recording material.
If the intake air amount of the negative pressure generator 407 is equal to or larger than an internal volume of the sub-tank 403, the air in the ink reservoir 436 is discharged through the gas-liquid separation member 433 and a new ink is fully replenished to the sub-tank 403 whatever the amount of the ink remaining in the ink reservoir 436 is. In this way, it suffices to absorb the air by a fixed amount or more so as to fully inject the ink. Therefore, it is unnecessary to conduct air discharge control. Besides, if the negative pressure generator is designed with a sufficient margin, it is basically possible to easily perform the ink replenishment operation.
As described above, according to the pit-in type ink jet recording apparatus that employs the gas-liquid separation member, the ink replenishment operation can be easily, stably performed. Further, by replenishing the ink whenever data is recorded on one sheet, it suffices that a usable ink amount held in the sub-tank is a sum of a necessary ink amount used for recording data on one recording sheet, the ink amount used for the recovery operation, and the ink amount used for the pre-discharge operation and that the ink reservoir is designed to be able to inject the total ink amount. Therefore, as compared with the conventional on-carriage type employing the head cartridge, it is possible to make the ink jet recording head small in size.
As described above, according to the pit-in type ink jet recording apparatus that employs the gas-liquid separation member, the head and the apparatus can be made small in size as compared with the conventional ink jet recording apparatuses.
Nevertheless, in order to further make the ink jet recording apparatus small in size, it is desired to further make the ink jet recording head, i.e., the sub-tank small in size.
To make the sub-tank small in size, it is considered to reduce the ink amount by which the ink is filled into the sub-tank. However, the ink amount necessary for recording data on the same recording material and those necessary for the recovery operation for preventing the poor discharge and the pre-discharge operation are constant irrespective of the type of the apparatus. Due to this, it is difficult to reduce the total ink amount. To make the sub-tank small in size, there is also proposed a method including improving an ink utilization efficiency of the ink filled into the sub-tank as high as possible and reducing the volume of the sub-tank.
Meanwhile, in the conventional ink jet recording head shown in FIG. 14, the porous ink absorbing member 437 is arranged in the ink reservoir almost entirely. By keeping the pressure of the ink acting on the discharge port negative using a capillary force of the porous member, it is advantageously possible to satisfactorily control the amount of the ink discharged from the ink jet recording head during recording and prevent the leakage of the ink from the discharge port while leaving the ink as it is. On the other hand, the conventional pit-in type ink jet recording apparatus has the following disadvantages. Since the ink absorbing member 437 is arranged in the ink reservoir, an ink filling amount is reduced by as much as a volume of the ink absorbing member and the ink remains in the ink absorbing member without being used after recording. As a result, the ink utilization efficiency is disadvantageously deteriorated (see FIG. 15A).
Further, the pit-in type ink jet recording apparatus which repeatedly performs recording and refilling has the following disadvantages. The apparatus generates an air accumulation in the ink absorbing member when the ink is refilled into the sub-tank. If the recording and refilling are repeated, the ink filling amount is reduced (see FIGS. 15B and 15C).
If the ink absorbing member is not arranged in the ink reservoir so as to solve these disadvantages, it is necessary to separately provide a mechanism that generates a negative pressure in the ink reservoir. The mechanism disadvantageously pushes up cost depending on a structure thereof and the sub-tank is disadvantageously made large in size.